Iolite
| Property | Details |
|---|
| Mineral | Cordierite |
| Mohs Hardness | 7 – 7.5 |
| Refractive Index | 1.542 – 1.551 |
| Birthstone | None (sometimes associated with September) |
| Major Sources | India, Sri Lanka, Madagascar, Tanzania |
| Treatments | Rarely treated |
Overview
Iolite is a transparent blue to violet-blue gemstone that offers a beautiful alternative to sapphire at a much lower price point. Also known as water sapphire, iolite displays a fascinating optical property called pleochroism—it shows different colors when viewed from different angles, shifting from blue-violet to yellowish-gray to near colorless.
History & Lore
Viking navigators reportedly used thin slices of iolite as polarizing filters to locate the sun on overcast days, earning it the nickname Viking's compass. This practical use of iolite's pleochroism made it an invaluable navigation tool centuries before the magnetic compass became common in Scandinavia.
Quality & Value Factors
The finest iolite displays a vivid violet-blue color without brownish or grayish tints. Because of its strong pleochroism, the cutter must orient the stone carefully to display the best blue-violet face-up color. Clarity should be eye-clean. Iolite is typically untreated, which appeals to gem purists. Its rich blue-violet color pairs beautifully with white gold and platinum settings.
Care & Cleaning
Iolite ranks 7 to 7.5 on the Mohs scale, making it suitable for most jewelry. Clean with warm soapy water and a soft brush. Avoid ultrasonic cleaners and sudden temperature changes.